Gold Mine Tectonics And Mineralize Regularities Of Jitoushan-Xiaoyanzigou Gold Deposits In Ningqiang County,Shaanxi Province

Jitoushan-Xiaoyanzigou gold deposits is situated in Ningqiang County,Shaanxi Province.It is also located geotectonically in the Bikou Block,which is the east edge of Motianling fold belt,Songpan-ganzi fold system.The deposits lies at the south part of Mian-lue-ning ore belt.And this region has a good geological condition of Mineralzation and also is rich in mineral resources.Most of the exposed strata in this area are the second subgroup of mid-upper Proterozoic Bikou group.The orientation of these stratum are almost EW,leaning to South.Protolith of Bikou group are intermediate-basic volcanic rocks,and geologically formed in island arc.Regional metamorphism made this rocks transformed to greenschist(e.g.sericite chorite quartz schist,chorite schist).The ore district is regionally located in Bahai ductile shear zone that lies with the orientation of NEE.Ore bodies lie in brittle.Up to now,there are four ore veins were found in this deposits,such as Au?,Au?,Au? and Au C2.These ore veins become thicker when their orientation changed in horizontal direction and their inclination have been flatter.The fault controlled the orientation of ore bodies forming like“double Y”type vertically.The major structure is disseminated structure.The country rock alterations are mainly silicatization,chloritization,epidotization and sericitization.Silicatization is closely related to the mineralization.The ignous rock that closely related to the mineralization is Yangba granitic mass,which lies outside of the deposits.It provides material for mineralization,shows that the rock is the production of magmation inIndo-Chinese epoch.Geochemical characteristics show that the rock is the I type granite.Geodynamics setting that forming Yangba granodiorite is the transition from sys-collision to post-collision.The ore body is controlled by fault structure,which is the main space form.It is a secondary high angle fracture structure in a large ductile shear zone in the mining area.Along the eastward enrichment zone of the strike belt in the eastern part of the fault belt,it is vertically enriched in the zone where the fault zone is slow,and the location of the corresponding change is generally the location of mineralization enrichment.According to the tectonic background,geological characteristics and the mineralizing condition of Jitoushan-Xiaoyanzigou gold deposits,we conclude that the deposits is the type of mesothermal hydrothermal vein deposit hosted in metamorphic rocks.It also can be classified as mesozonal orogenic gold deposits,proposed by Groves(1998).